/Engine/Source/Runtime/SlateCore/Public/Textures/TextureAtlas.h
Finds a currently occupied slot at a position specified in atlas coordinates where 0,0 is the top left and the size of the atlas is bottom right
[FAtlasSlotInfo](API\Runtime\SlateCore\Textures\FAtlasSlotInfo) GetAtlasSlotInfoAtPosition ( FIntPoint InPosition, int32 AtlasIndex ) const